1. Field of the Invention
The present disclosure relates to spring-applied parking brakes for railway vehicles which normally are released by use of pneumatic pressure. This disclosure further relates to manual release and reapplication of the parking brake, for example, using a ball screw reset mechanism.
2. Description of Related Art
Service brakes for railway vehicles are normally applied by pneumatic cylinders supplied with pressurized air by a lead locomotive or engine. When the railway vehicle is separated from the lead locomotive, such as during the process of composing a train, a parking brake is desirable to prevent runaway motion of the railway vehicle. Typically, the parking brake is spring applied. Pushrods connected to spring-actuated pistons connect with linkages to effect braking function when the railway vehicle is not coupled to the lead locomotive. The spring-applied brakes can be released by pneumatic pressure once the vehicle is reconnected to a lead vehicle or a source of pressurized air.
In some prior art spring-applied brakes, a manual release is provided for disconnecting the piston from the pushrod, thus permitting movement of the vehicle. In other prior art, the application and release of the parking brake force is effected with either air pressure or with a mechanical winding action. In this case, the connection between the spring-driven piston and the pushrod is controlled by a nut threaded on the pushrod, the rotation of which is caused by a manual means, such as a hand wheel. This arrangement utilizes a conventional threaded connection between the nut and the pushrod, thereby requiring a significant manual input in order to actuate the manual release of the spring-applied brake. In certain embodiments, over 40 rotations of the hand wheel may be necessary before the spring-applied force is released and the railway vehicle may be moved. This process is very inefficient and requires a substantial amount of time and manual exertion. Additionally, conventional spring-applied brakes take a significant amount of time to manually apply or release. Accordingly, there is a need in the art for a spring-applied railway vehicle parking brake that overcomes the various inefficiencies of the prior art.